WO2023243396A1 - Fibres courtes, liquide dispersé dans des fibres et tissu non tissé - Google Patents

Fibres courtes, liquide dispersé dans des fibres et tissu non tissé Download PDF

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Publication number
WO2023243396A1
WO2023243396A1 PCT/JP2023/020061 JP2023020061W WO2023243396A1 WO 2023243396 A1 WO2023243396 A1 WO 2023243396A1 JP 2023020061 W JP2023020061 W JP 2023020061W WO 2023243396 A1 WO2023243396 A1 WO 2023243396A1
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Prior art keywords
fibers
fiber
nonwoven fabric
short
short fibers
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PCT/JP2023/020061
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English (en)
Japanese (ja)
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達也 石川
知彦 松浦
正人 増田
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東レ株式会社
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    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
    • D01F6/58—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products
    • D01F6/62—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products from polyesters
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F8/00—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof
    • D01F8/04—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof from synthetic polymers
    • D01F8/14—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof from synthetic polymers with at least one polyester as constituent
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H15/00—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution
    • D21H15/02—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution characterised by configuration

Definitions

  • the present invention relates to short fibers, fiber dispersions, and nonwoven fabrics, and more specifically, short fibers suitable for fiber dispersions, fiber dispersions in which the short fibers are dispersed in an aqueous medium, and complex voids made of the short fibers.
  • the present invention relates to a nonwoven fabric having a special structure in which
  • Fibers have various characteristics derived from their thin and long form, so they are used not only for clothing but also for industrial materials. There has been a growing demand for textile products with advanced functions.
  • One of the characteristics derived from the morphology of fibers is that they have a large specific surface area, which is the surface area per unit weight.By utilizing this specific surface area, it is possible to achieve a high adsorption effect on target substances and a high adsorption effect when added as a filler. Since fibers can provide reinforcing effects, research is underway into a wide variety of high-performance materials that take advantage of the specific surface area of fibers.
  • fiber dispersion in which short fibers cut to a desired length are dispersed in a medium, and this dispersion itself can be used as an adsorbent or as a filler for resin products. Not only can it be used for introduction, but it can also be used as a high-performance filter medium or separation membrane by cutting the dispersion liquid using a wet paper-making method and forming it into a sheet.
  • Technology development is actively underway.
  • An indicator that determines the performance of this fiber dispersion is that the fibers are homogeneously dispersed in the dispersion and can fully utilize their specific surface area, but due to the specific surface area of the mixed fibers, the fibers are In addition to being prone to agglomeration, thin and long fibers tend to become intertwined in the first place, making the dispersion state inhomogeneous.
  • Various techniques have been proposed.
  • Patent Document 1 proposes a technique for producing ultrafine fibers that is advantageous for enhancing the specific surface area effect.
  • ultrafine fibers With ultrafine fibers, the cohesive force derived from intermolecular forces increases dramatically due to the increase in specific surface area, making it difficult to obtain a homogeneous dispersion.
  • by extremely shortening the fiber length to less than 1 mm This makes it possible to uniformly disperse the fibers in the dispersion liquid without causing a lump-like dispersion failure in which the fibers are entangled.
  • Patent Document 2 relates to a technology that improves the dispersibility of fibers by actively causing electrical repulsion to act between ultrafine fibers, and the electrical repulsion that acts between the fibers is made stronger than the cohesive force. By increasing the fiber length, homogeneous dispersion can be achieved even when the fiber length is long.
  • Patent Document 3 is a technology that aims at homogeneous dispersion in a dispersion liquid by processing short fibers in the longitudinal direction to make them uniformly dispersed in the dispersion liquid due to their morphological characteristics. This makes it possible to suppress the occurrence of poor dispersion in the form of lumps in which fibers are entangled.
  • Patent Document 1 discloses that as the fiber diameter becomes smaller, the fibers become softer and more easily bent, and the fibers tend to become intricately entangled in the dispersion liquid, resulting in poor dispersion in the form of lumps. This takes advantage of the fact that it becomes difficult for the two to become entangled.
  • the fibers are less likely to get entangled in the dispersion liquid.
  • this method can achieve a homogeneous dispersion state during low-speed stirring, During high-speed stirring, poor dispersion due to entangled fibers is likely to occur, and dispersibility may become an issue. In particular, this poor dispersion tends to be noticeable in ultrafine fibers, and the processes that can be applied to prepare a dispersion of ultrafine fibers are sometimes limited.
  • Patent Document 2 by utilizing the electrical repulsive force between the fibers, the repulsive force acts between the fibers, resulting in homogeneous dispersion, making it difficult to settle, and maintaining the dispersed state for a long period of time. If a force greater than electrical repulsion is applied, the fibers may come into contact and form a fiber mass, which may limit the steps that can be applied to form a dispersion.
  • Patent Document 3 discloses that by tearing ultra-fine fibers using a roll press, they are made into ultra-fine flat short fibers with uneven thickness in the longitudinal direction, and a portion of the short fibers becomes thick and difficult to bend, making it difficult for the fibers to become entangled. It is something.
  • the upper limit for the difference in thickness in the longitudinal direction of a single short fiber is about twice, and after all, during high-speed agitation, the fibers may become entangled with each other and form fiber clumps. There were cases where dispersibility became an issue.
  • short fibers with a high specific surface area can be homogeneously dispersed when left standing or stirred at low speeds, but they cannot be homogeneously dispersed even when stirred at high speeds.
  • There is no technology for dispersing fibers and the manufacturing process for fiber dispersions has been limited. Therefore, in response to recent demands, there has been a desire for short fibers that can be applied to a wide range of processes, can be deployed in various fields of use, and have excellent dispersibility and are suitable for fiber dispersions.
  • the present invention has the following configuration. That is, (1) Short fibers whose flatness, which is the value obtained by dividing the length of the major axis of the fiber cross section by the length of the minor axis, is 5 or more, and the average length of the minor axis is 2,000 nm or less. (2) The short fiber according to (1), in which the length variation (CV value) of the short axis of the fiber cross section is 10% or more. (3) The short fiber according to any one of (1) or (2), wherein the degree of unevenness of the fiber cross section is 20% or more. (4) The short fiber according to (1), which has a crystallinity of 20% or less. (5) The short fiber according to (4), which has a melting point of 180°C or higher.
  • Ra arithmetic mean roughness
  • the present invention relates to short fibers that exhibit excellent dispersibility in liquid media such as water due to the highly flattened fiber cross section, and the short fibers do not become entangled even under a wide range of stirring conditions. It is possible to provide a homogeneous fiber dispersion. In addition, by making use of the excellent water dispersibility of these short fibers and forming them into a sheet, it is possible to obtain a nonwoven fabric with a special structure in which dense yet complex voids are formed. It exhibits excellent properties in absorbing sound in the low frequency range related to road noise and filtering and separating specific components, and is expected to be widely used as an industrial material.
  • FIG. 1 is a schematic diagram of an example of a cross-sectional structure of short fibers of the present invention.
  • FIG. 2 is a schematic diagram of a cross-sectional structure for explaining the unevenness of short fibers of the present invention.
  • FIG. 1 is a schematic diagram of an example of a cross-sectional structure of a multilayer laminated fiber used as a raw material for short fibers of the present invention.
  • FIG. 2 is a cross-sectional view for explaining an example of a method for manufacturing multilayer laminated fibers.
  • FIG. 1 is a schematic diagram of an example of a cross-sectional structure of short fibers of the present invention.
  • FIG. 2 is a schematic diagram of a cross-sectional structure for explaining the unevenness of short fibers of the present invention.
  • FIG. 1 is a schematic diagram of an example of a cross-sectional structure of a multilayer laminated fiber used as a raw material for short fibers of the present invention.
  • FIG. 2 is a cross-sectional view for
  • FIG. 2 is a characteristic diagram showing the brightness histogram of a fiber dispersion liquid made of short fibers of the present invention, in which (a) is a schematic view of the brightness histogram of a fiber dispersion liquid in which fibers are homogeneously dispersed, and (b) is a diagram showing the brightness histogram of a fiber dispersion liquid in which fibers are homogeneously dispersed; It is a schematic diagram of the brightness histogram of the fiber dispersion liquid when.
  • the present invention relates to short fibers characterized by excellent dispersibility in liquid media such as water, and the short fibers referred to in the present invention refer to short fibers having a fiber length of less than 100 mm and extending along the longitudinal direction of the fibers. Refers to fibers that are cut to the desired length.
  • the short fibers of the present invention utilize their high specific surface area to exhibit a high adsorption effect on target substances and a high reinforcing effect when added as a filler.
  • the specific surface area of the short fibers is preferably 0.0010 nm -1 or more from the viewpoint of improving their performance.
  • a fiber bundle made of the short fibers of the present invention is embedded in an embedding agent such as an epoxy resin, and a cross section of the fiber is cut out using a microtome equipped with a diamond knife, and this cross section is examined using a scanning electron microscope (SEM). Take pictures at a magnification that allows you to distinguish the cross section.
  • an embedding agent such as an epoxy resin
  • Specific surface area (nm ⁇ 1 ) outer circumference length (nm) / cross-sectional area (nm 2 )
  • the above measurements are performed on 100 fibers to calculate the specific surface area of each fiber, and the arithmetic mean of these is taken as the specific surface area.
  • the specific surface area is 0.0010 nm -1 or more, a specific surface area effect equivalent to that of ultrafine fibers with a fiber diameter of several ⁇ m can be exhibited, and excellent adsorption performance can be exhibited.
  • the effect of the present invention becomes more pronounced, and if the specific surface area is 0.0040 nm -1 or more, the effect is equivalent to that of nanofibers with a fiber diameter of several hundred nm.
  • This range can be cited as a more preferable range because it exhibits the following effects.
  • the short fibers of the present invention are characterized by excellent dispersibility in liquid media such as water, which has not been achieved with conventional techniques.
  • An important requirement for achieving both the specific surface area of short fibers and excellent dispersibility is that the flatness, which is the value obtained by dividing the length of the long axis of the fiber cross section by the length of the short axis, must be 5 or more. This is the first requirement of the present invention.
  • Flatness length of major axis (nm) / length of minor axis (nm) The above measurements are performed on 100 fibers to calculate the flatness of each fiber, and the arithmetic mean of these is taken as the flatness.
  • the short fibers of the present invention need to have a flatness of 5 or more. In this range, the bending stiffness in the short axis direction and the long axis direction will be significantly different due to the morphological characteristics of the cross section, that is, the shape anisotropy of the cross section, and when it is made into a fiber dispersion, the short fibers
  • the bending direction is limited to the short axis direction. Due to this restriction on the direction of deformation, even if the short fibers come into contact with each other in the dispersion, the short fibers will not bend and become intricately intertwined, resulting in poor dispersion. It exhibits dispersibility.
  • the short fibers of the present invention are difficult to entangle with each other in the dispersion by limiting the bending direction using the shape anisotropy of the cross section.
  • the higher the flatness the larger the difference in bending rigidity between the short axis direction and the long axis direction, and when used as a fiber dispersion, the bending direction will be firmly restricted to the short axis direction.
  • the flatness is 15 or more, the bending rigidity will differ by a factor of 200 or more between the short axis direction and the long axis direction of the cross section, and the bending direction of the short fibers in the dispersion is essentially limited to only the short axis direction. It will be done.
  • the short fibers are difficult to entangle with each other in the dispersion even when stirred at high speed, and exhibit excellent dispersibility, so the flatness can be reduced. It is preferable that it is 15 or more.
  • the flatness is 30 or more, even under high-speed stirring conditions where high shear force is applied to defibrate short fiber bundles aggregated by cohesive forces such as intermolecular forces, the cross-sectional shape anisotropy will be maintained. Due to the restriction on the bending direction caused by this, it becomes difficult for short fibers to become entangled with each other after defibration. From the viewpoint of obtaining excellent dispersibility under a wide range of stirring conditions including fibrillation, the flatness is more preferably 30 or more.
  • the flatness is 50 or more, due to the remarkable shape anisotropy, when the fiber dispersion is stirred, the short axis direction of the short fiber cross section is aligned due to the flow velocity difference in the dispersion. It becomes easier to assume a fluid state. In such a fluid state, it is particularly preferable that the flatness is 50 or more because the short axes are aligned, making it difficult for the short fibers to come into contact with each other, and making it easier to achieve a homogeneous dispersion state.
  • the short fibers of the present invention bend in the dispersion liquid from all 360° directions to only the short axis direction. This makes it difficult to form dispersion defects in the form of lumps in which the short fibers are intricately intertwined with each other, and even short fibers with a high specific surface area can exhibit excellent dispersibility under a wide range of stirring conditions.
  • the dispersibility of these short fibers is affected not only by the flatness of the cross section but also by the fiber diameter, and under a wide range of stirring conditions from low to high speeds, the dispersibility derived from the cross-sectional shape can be sufficiently improved.
  • the fiber diameter is also an important requirement.
  • the second requirement for the short fibers of the present invention is that the length of the short axis of the cross section is short, and the average length of the short axis must be 2,000 nm or less.
  • the average short axis length referred to here is determined by rounding off the arithmetic mean of the short axis lengths of the 100 fibers measured above to an integer in nanometers.
  • the sedimentation rate of the fibers in the dispersion liquid will be sufficiently slow, and the dispersed state of the fibers will be maintained homogeneously.
  • the shorter the length of the short axis the slower the sedimentation speed of the fiber becomes, making it difficult for the fiber to settle over time. Therefore, in the short fiber of the present invention, the average length of the short axis is It is preferable that the particle diameter is 1,000 nm or less, and within this range, even when stirring is performed with a weak force, the fibers will not settle and a homogeneous dispersion state can be maintained.
  • the average length of the short axis is 250 nm or less; within this range, even when the fiber dispersion is stored and no stirring force is applied for a long time, the fibers are difficult to settle. A homogeneous dispersion state will be maintained.
  • the average short axis length of the short fibers of the present invention is 20 nm or more as a range in which it is difficult to break when external force is applied during a stirring process, etc., and the practical lower limit in the present invention value.
  • the short fibers of the present invention have an ultra-flat cross section in which the long axis is extremely long with respect to the short axis, so that the bending direction of the short fibers themselves is restricted, and they can be immersed in liquid media such as water.
  • the range of conditions under which a homogeneous dispersion state can be maintained is much wider than that of conventional techniques, such as by allowing a wide range of stirring conditions from high shear to low shear.
  • the fiber cross section has a distribution within a certain range. Therefore, in the short fibers of the present invention, it is preferable that the lengths of the short axes vary.
  • the variation in short axis length is calculated by calculating the arithmetic mean and standard deviation using the short axis lengths of the 100 fibers measured above, and dividing the standard deviation by the arithmetic mean.
  • the short fibers of the present invention it is preferable that the variation in short axis length is 10% or more, and by setting it within this range, a high concentration of short fibers with which the fibers are likely to come into contact with each other is added. Even in the dispersion liquid, since the bending behavior and the like are different for each fiber, entanglement does not occur and a homogeneous dispersion state can be ensured.
  • the short fibers are less likely to become entangled, and the short fibers can be diluted with liquid.
  • This can be cited as a more preferable range in the present invention because excellent dispersibility can be achieved by doing so.
  • the variation in the short axis length is 30% or more, and within this range, when short fibers are dispersed in a medium from aggregated short fiber bundles or fiber aggregates. Even so, the short fibers exhibit different behaviors and break apart due to external force, which eliminates the agglomerated state and makes it possible to easily disperse the fibers by stirring for a short time.
  • the unevenness on the outer periphery of the flat cross section suppresses adhesion and entanglement between the short fibers due to steric hindrance. It is preferable that the degree of unevenness in the fiber cross section is 20% or more.
  • the degree of unevenness refers to the length at which a line segment perpendicular to the maximum length of the cross section intersects with the fiber cross section at a point where the maximum length of the cross section is divided into 10 equal parts using an image of the fiber cross section taken. Then, calculate the arithmetic mean and standard deviation of the lengths of these 10 points, divide the standard deviation by the arithmetic mean, and round off to the nearest whole decimal point to determine the unevenness of the single fiber (see Figure 2). reference). Similar measurements are performed on the cross sections of 10 fibers, and the arithmetic mean of the calculated unevenness of the 10 fibers is defined as the unevenness here. When the degree of unevenness is 20% or more, the short fibers can be easily dispersed starting from the minute voids between the fibers, and can be uniformly dispersed in a short time.
  • a high degree of unevenness suppresses entanglement between short fibers, but the range where the load does not concentrate on a part of the cross section and cause cracks is when the degree of unevenness is 50% or less. This can be cited as a practical upper limit in the invention.
  • the short fibers of the present invention have a high specific surface area effect and excellent dispersibility that allows the effect to work effectively due to the fiber cross section, and when added as a filler to a resin. By making it into a sheet, it can be used as a highly functional nonwoven fabric with performance such as separation, filtration, and adsorption.
  • the sheet When made into a non-woven fabric, the sheet exhibits its mechanical properties due to the bridging structure created by the frictional force between adjacent short fibers, but this bridging structure means that the short fibers present in the medium Therefore, when there are short fibers at the same concentration in the medium, the thinner the fiber diameter and the longer the fiber length, the more a bridging structure is formed and the force is transmitted. will be promoted. In other words, the higher the ratio of fiber length to fiber diameter, the more the formation of a bridge structure is promoted, and as an indicator of this, the aspect ratio, which is the value obtained by dividing the fiber length by the length of the short axis, is used as an indicator for the short fibers of the present invention. It can be said that it is preferable that the value is high.
  • the aspect ratio referred to in the present invention is determined as follows.
  • An image of the fiber bundle made of the short fibers of the present invention is photographed using a microscope at a magnification that allows observation of 10 or more short fibers whose total length can be measured.
  • the fiber length of 10 short fibers randomly extracted from an image of the short fibers is measured.
  • the fiber length here refers to the length of a single fiber in the longitudinal direction from a two-dimensionally photographed image, and is measured using image analysis software (WINROOF), rounded to the second decimal place. It is.
  • WINROOF image analysis software
  • the above operation is performed for 10 similarly photographed images, and the arithmetic average of the fiber lengths of 100 fibers is taken as the fiber length of the present invention.
  • the aspect ratio is calculated by rounding off to the nearest whole number according to the following formula.
  • Aspect ratio fiber length (nm) / average short axis length (nm)
  • the aspect ratio is preferably 3,000 or more, and within this range, a bridging structure is sufficiently formed between the short fibers, and the binder Even when no reinforcement is performed, the obtained nonwoven fabric exhibits mechanical properties at a level that poses no problem in actual use.
  • the aspect ratio of the short fibers is 6,000 or more, and within this range, when formed into a sheet, it not only exhibits sufficient mechanical properties, but also facilitates the sheet forming process. It also has excellent processability, such as minimizing the shedding of short fibers.
  • the aspect ratio of the short fibers is preferably 50,000 or less, as long as the short fibers do not become entangled in the dispersion and can ensure good handling without any restrictions on stirring conditions, etc. This is a practical upper limit for the invention.
  • the polymer constituting the short fibers of the present invention is preferably a polymer with excellent heat resistance and chemical resistance, considering the desired effects of the present invention and practical use as a textile product. That is, it is preferable that the polymer constituting the short fibers consists of at least one kind of polymer selected from the group of polyester, polyamide, polyphenylene sulfide, and polyolefin.
  • the short fibers of the present invention can not only be produced by a highly productive melt spinning method, but also have improved mechanical properties such as highly oriented crystallization during the drawing process. This is suitable from the viewpoint of adjustment.
  • the short fibers of the present invention are preferably composed of a polymer with high elastic modulus such as polyester or polyphenylene sulfide, which suppresses bending of the fibers when external force is applied. Therefore, in the step of dispersing short fibers, it is possible to effectively suppress the occurrence of poor dispersion caused by entanglement of fibers.
  • a homogeneous dispersion state can be achieved without causing repulsion between the fibers and causing agglomeration. It becomes easier.
  • the short fibers of the present invention are preferably dispersed in a medium to form a fiber dispersion.
  • the medium is an aqueous medium.
  • the short fibers of the present invention are homogeneously dispersed under a wide range of stirring conditions from high shear to low shear when dispersed in a liquid medium such as water due to the cross-sectional shape anisotropy. condition can be maintained.
  • a liquid medium such as water due to the cross-sectional shape anisotropy. condition can be maintained.
  • the short fibers can be laid out in a uniformly dispersed state, and the short fibers will not be unevenly distributed. As a result, it is possible to obtain a nonwoven fabric with a special structure in which dense yet complex voids are formed.
  • the short axis direction of the cross section is naturally aligned with the thickness direction of the nonwoven fabric, and they are piled up densely, resulting in homogeneous dispersion. Combined with the state effects, this results in the formation of special structures that cannot be achieved with conventional techniques. For this reason, it is preferable to use a nonwoven fabric containing the short fibers of the present invention.
  • the nonwoven fabric of the present invention is characterized by having a special structure in which complex voids are formed inside while being dense, and the first requirement is that the nonwoven fabric density is 0.4 g/cm 3 or more.
  • the nonwoven fabric density as used in the present invention is determined as follows.
  • the basis weight of the nonwoven fabric is determined by weighing the nonwoven fabric cut into a 250 mm x 250 mm square, rounding the value converted to weight (g) per unit area (1 m 2 ) to the first decimal place, and determining the thickness using the dial. Measurement is performed in mm using a thickness gauge SM-114 (manufactured by TECLOCK, measuring head shape 10 mm ⁇ , scale interval 0.01 mm, measuring force 2.5 N or less). This is performed at five arbitrary locations for each sample, and the average value is rounded to the third decimal place and the value determined to the second decimal place is taken as the thickness of the nonwoven fabric.
  • a thickness gauge SM-114 manufactured by TECLOCK, measuring head shape 10 mm ⁇ , scale interval 0.01 mm, measuring force 2.5 N or less. This is performed at five arbitrary locations for each sample, and the average value is rounded to the third decimal place and the value determined to the second decimal place is taken as the thickness of the nonwoven fabric.
  • the nonwoven fabric density calculates the nonwoven fabric density according to the following formula. This is determined for 10 samples, and the value obtained by rounding off the simple average value to the third decimal place is defined as the nonwoven fabric density.
  • Nonwoven Fabric Density (g/cm 3 ) Basic Weight/Thickness
  • the nonwoven fabric of the present invention needs to have a nonwoven fabric density of 0.4 g/cm 3 or more. By setting it within this range, even if the thickness of the nonwoven fabric is sufficiently thin, it has a dense structure with few voids included in the nonwoven fabric, so when used as a sound absorbing material, it is expected that the sound absorption coefficient will improve in the low frequency band. Can be done. Assuming that the thickness of the nonwoven fabric is further reduced and it is placed in a limited space, such as for use as an exterior material for a vehicle interior, it is preferable that the density of the nonwoven fabric is 0.6 g/cm 3 or more.
  • the sheet is very thin, the nonwoven fabric of the present invention has voids penetrating the sheet that are suitable for the sound absorption mechanism, so that the objective of the present invention can be achieved without reflecting the sound that should be absorbed. can be demonstrated.
  • the above-mentioned nonwoven fabric density can be achieved by appropriately adjusting the sheet thickness and basis weight on the premise that each fiber constituting the sheet exists in a dispersed state. At this time, by setting the basis weight of the sheet to a certain level, it is possible to form microscopic spaces of the desired size, and a nonwoven fabric that maintains the strength of a practical sheet can be obtained. From the above viewpoint, it is preferable that the nonwoven fabric of the present invention has a basis weight of 3 to 500 g/ m2 , and within this range, each fiber is stably and homogeneously present without impairing the objective effect of the present invention. It becomes a sheet.
  • the second requirement for the special structure of the nonwoven fabric of the present invention is that the average pore size is 6 ⁇ m or less, and the maximum frequency of pore size distribution is 30% or less.
  • the pore size here refers to the value calculated by the bubble point method.
  • a porous material automatic pore measurement system Perm-Porometer manufactured by PMI
  • PMI porous material automatic pore measurement system
  • a nonwoven fabric is immersed in a liquid with a known surface tension value, and gas pressure is supplied from above the sheet while increasing, and the pore size is determined from the relationship between this pressure and the liquid surface tension on the surface of the nonwoven fabric. Measure.
  • the pore size is calculated using a porous material automatic pore measurement system Perm-Porometer (manufactured by PMI).
  • the frequency of the pore size distribution was expressed as a percentage by converting the value obtained by automatic calculation into a percentage, and the value at which the frequency of the pore size distribution was maximum was taken as the maximum frequency. Then, the average of the maximum frequencies of each sample is calculated, and the value obtained by rounding off the second decimal place to the first decimal place is used.
  • the nonwoven fabric of the present invention needs to have an average pore size of 6 ⁇ m or less and a maximum frequency of pore size distribution of 30% or less. Within this range, the size of the voids contained within the nonwoven fabric is small and there are various void sizes. Therefore, when used as a sound absorbing material, the complex void structure allows sound absorption over a wide range of low frequency bands.
  • the average pore size is 2 ⁇ m or less and the maximum frequency of pore size distribution is 20% or less.
  • the lower limit for substantially fully achieving the object of the present invention is that the average pore size is 0.1 ⁇ m or more and the maximum frequency of pore size distribution is 10% or more, and within this range, the fluid is inhibited. effective sound absorption performance can be achieved without
  • the nonwoven fabric of the present invention exhibits excellent properties even when used alone as a sound absorbing material, but when it is assumed that it will be used in sound absorbing materials for electric vehicles, which have been developed rapidly in recent years, it will be possible to combine it with other materials. It is envisioned that it will be used as a laminated material. In this case, when manufacturing the molded article, it will be bonded to other materials using a binder, so in terms of increasing the bonding strength with other materials, the nonwoven fabric of the present invention has an arithmetic average of the surface of the nonwoven fabric. It is preferable that the roughness (Ra) is 5.0 ⁇ m or less.
  • the arithmetic mean roughness (Ra) referred to here is determined as follows. That is, the surface of the nonwoven fabric was observed using a laser microscope (VK-X200 manufactured by Keyence Corporation or a laser microscope with equivalent performance), and analyzed using analysis software (VK-H1XA manufactured by Keyence Corporation or a laser microscope with equivalent performance). Measurement is performed in accordance with JIS B 0601 using analysis software (with analysis software). This is performed at five arbitrary locations for each sample, and the average value is rounded off to the third decimal place and the value obtained to the second decimal place is set as Ra.
  • the value of the arithmetic mean roughness (Ra) of the surface of the nonwoven fabric of 5.0 ⁇ m or less means that it has sufficient smoothness to exhibit practical characteristics, and there is no roughness on the surface. Since there are no irregularities, it is possible to perform integral molding by bonding with other materials, etc., and it has excellent resistance to peeling over time. Furthermore, within this range, it exhibits a favorable effect from the perspective of sound absorption. For example, when the nonwoven fabric of the present invention is used as a sound absorbing material, it suppresses the diffuse reflection of sound waves on the surface and effectively absorbs sound. becomes possible. From this point of view, in order to further suppress the diffuse reflection of sound waves on the surface, it is more preferable that the arithmetic mean roughness (Ra) of the surface of the nonwoven fabric is 2.0 ⁇ m or less.
  • the special structure of the nonwoven fabric of the present invention which is dense yet has complicated internal voids, it can be used as a sound absorbing material to exhibit excellent sound absorption performance mainly in the low frequency band.
  • a wide range of sound absorption performance can be achieved by designing the sheet structure and combining it with other materials.
  • the special sheet structure formed in the nonwoven fabric of the present invention is excellent not only for general filtration, but also for adsorption and filtration of valuables and harmful substances, and can be effectively used as a base material for filter media. can.
  • a wet method that is good at producing highly dense nonwoven fabrics that is, a wet papermaking method, is preferably used to form the dense structure that is a feature of the nonwoven fabric of the present invention. This makes it possible to stably manufacture the special sheet structure that is a feature of the present invention.
  • the special structure in which dense yet fine voids are formed which is a feature of the nonwoven fabric of the present invention, makes it possible to adjust the mixing ratio of the various fibers that make up the nonwoven fabric and change the cross-sectional form of the short fibers of the present invention. By doing so, it can be adjusted as appropriate.
  • the higher the flatness of the fiber cross section the more pronounced the effect of laying the fiber cross sections in the same direction, and the smaller the length of the short axis of the fiber cross section, the more flexible it is in the short axis direction.
  • the nonwoven fabric Since the nonwoven fabric is bent and blends better with other mixed materials, a nonwoven fabric with a denser and more complex pore structure can be obtained.
  • the variation in the length of the short axis of the fiber cross section and the degree of unevenness are large to some extent, which acts as a steric hindrance within the nonwoven fabric, creating fine voids between the short fibers, which is a characteristic of the nonwoven fabric of the present invention. Special structures can be made noticeable.
  • the short fibers with a high specific surface area exist homogeneously without uneven distribution, but the direction of the flat cross section is aligned and the nonwoven fabric is dense.
  • the contact area between fibers within the nonwoven fabric increases dramatically.
  • the short fibers of the present invention constituting the nonwoven fabric as binder fibers responsible for adhesion between fibers within the nonwoven fabric, it is possible to exhibit excellent adhesion even in thin and low basis weight nonwoven fabrics, and improve mechanical properties.
  • a thin nonwoven fabric with excellent properties can be obtained.
  • the degree of crystallinity is preferably 20% or less from the viewpoint of exhibiting excellent thermal adhesiveness.
  • thermal adhesiveness refers to the ability to soften and flow by heating, adhere to adherends, and then cool and solidify to bond and bond the adherends together.
  • the contact area between the fibers is large due to the morphological characteristics of the fibers, and in addition, the fibers exhibit thermal adhesive properties, so that the fibers can be firmly bonded. , it becomes possible to increase the strength of the nonwoven fabric.
  • This thermal adhesiveness is also affected by the state of impregnation of short fibers at each bonding point, and fluidity of the fibers is also an important requirement in order to fully exhibit thermal adhesiveness.
  • the short fibers of the present invention preferably have a crystallinity of 20% or less.
  • the crystallinity referred to here is determined as follows.
  • the fibers were set in a differential scanning calorimeter (DSC), and differential scanning was performed under nitrogen at a heating rate of 16°C/min and a measurement temperature range of 50 to 320°C. Perform scanning calorimetry.
  • DSC differential scanning calorimeter
  • the heat of crystallization ⁇ Hc (J/g) is calculated from the area of the exothermic peak in the obtained measurement results (DSC curve), and the heat of crystallization ⁇ Hm (J/g) is calculated from the area of the endothermic peak.
  • ⁇ Hc and ⁇ Hm are calculated from the sum of the areas of all the peaks. Measurement is performed three times by changing the measurement position for each level, and after calculating the arithmetic mean and calculating ⁇ Hc and ⁇ Hm, the degree of crystallinity is calculated by rounding to the first decimal place using the following formula.
  • Crystallinity (%) ( ⁇ Hm- ⁇ Hc)/ ⁇ Hm 0 ⁇ 100 Note that ⁇ Hm 0 referred to here is the heat of fusion of a complete crystal (J/g).
  • the amorphous region is not easily inhibited by the crystalline region and can be sufficiently softened and fluidized when heated above the glass transition temperature of the short fiber.
  • the softened and fluidized short fibers can enter between the bonded materials and exhibit high thermal adhesiveness.
  • the short fibers of the present invention should have a degree of crystallinity of 15% or less. is more preferable, and within this range, it can easily penetrate into the complex irregularities of the adherend without any gaps, and exhibit excellent thermal bonding properties regardless of the shape of the adherend.
  • the degree of crystallinity is 10% or less, and within this range, the softened and fluid short fibers can easily get between the material to be adhered and the material to be bonded even when the heat press pressure of calendering is low. Therefore, it is possible to reduce adhesion to the roller during hot pressing and reduce process tension, and it is possible to suppress breakage during the manufacturing process of thin, low basis weight sheet materials.
  • the degree of crystallinity is 8% or less, and if the crystallinity is in this range, even if non-contact heating such as an oven without calendar processing is used, the thermoplastic fibers will soften and flow, and the bonded material will be It can fit between the two and exhibit excellent thermal adhesion.
  • the short fibers of the present invention not only have the effect of increasing the adhesion area due to the morphological characteristics of the fibers, but also have good fluidity during heating due to the fiber structure, which allows the thermoplastic fibers to bond with the bonded material. It penetrates without any gaps and exhibits excellent thermal adhesion, making it possible to achieve excellent mechanical properties in thin, low basis weight sheet materials, which was difficult to achieve with conventional technology. .
  • the adhesive penetrates not only the macroscopic unevenness between the bonded materials but also the minute unevenness at the bonding point without any gaps at the molecular level.
  • the peak value of tan ⁇ of the short fibers of the present invention is 0.10 or more.
  • the tan ⁇ here refers to using a dynamic viscoelasticity automatic measuring device (Rheo Vibron), holding the sample at a distance of 30 mm between chucks, applying a tension of 0.07 g/dtex, and heating at a heating rate of 3°C/min. The measurement is performed at a frequency of 110 Hz.
  • Ro Vibron dynamic viscoelasticity automatic measuring device
  • the peak value of tan ⁇ corresponds to the amount of molecular chains that can move without restriction at that temperature, and the larger this value, the easier the material will flow at that temperature. If it is 0.10 or more, the softened and fluid short fibers can easily enter between the bonded materials, and the bonded materials can be firmly bonded, so it can be cited as a preferable range.
  • the peak value of tan ⁇ is 0.15 or more, since the softened and fluidized short fibers can easily enter the irregularities on the surface of the adhered material, and the separation of the short fibers adhered to the adhered material can be suppressed. It can be mentioned as a range. If the peak value of tan ⁇ is 0.20 or more, it can penetrate into the minute irregularities on the surface of the bonded material at the molecular level, and the peeling of the short fibers bonded to the bonded material can be significantly suppressed, so this is a more preferable range. can be mentioned.
  • the polymer constituting the short fibers of the present invention is preferably a polymer with excellent heat resistance, considering its actual use as a sheet-like article or textile product, and the melting point of the polymer constituting the short fibers of the present invention is 180. It is preferable that the temperature is °C or higher.
  • the melting point of the polymer mentioned here is determined as follows.
  • the polymer was reduced to a moisture content of 200 ppm or less using a vacuum dryer, weighed out to be about 5 mg, heated from 0°C to 320°C at a rate of 16°C/min using a differential scanning calorimeter (DSC), and then heated at 320°C. Hold for 5 minutes and perform DSC measurement.
  • the melting point is calculated from the melting peak observed during the heating process. Measurement is performed three times for each sample, and the arithmetic average thereof is taken as the melting point of the polymer of the present invention. In addition, when multiple melting peaks are observed, the top of the melting peak on the highest temperature side is taken as the melting point.
  • the melting point of the polymer constituting the short fibers of the present invention is 180°C or higher, even when a sheet-like product made of the short fibers is used after being processed in various ways, the short fibers are exposed to heat during the processing process.
  • This range can be cited as a preferred range because the fibers are less likely to soften and lose their adhesive strength and exhibit excellent process passability.
  • the melting point of the polymer constituting the short fibers is 200°C or higher, even when applying or coating other thermoplastic resins with low melting points, the mechanical and physical properties of the sheet material are improved due to the softening of the bonding points.
  • This range can be cited as a more preferable range because it is less likely to be damaged and can pass through the process well.
  • the melting point of the polymer constituting the short fibers is 220°C or higher, even when the tension is high during the heat-applying process described above, the bonding points can maintain a sufficiently solidified state, which improves mechanical properties.
  • This range can be cited as a more preferable range since various processes can be applied without impairing physical properties.
  • the short fibers of the present invention maintain an amorphous state before the thermal bonding process and are thermally crystallized after the thermal bonding process, thereby achieving strong thermal bonding during low-temperature heat treatment while maintaining sufficient strength for practical use.
  • examples of polymers include polyethylene terephthalate or its copolymers, polyethylene naphthalate, and polyphenylene sulfide.With these polymers, the undrawn yarn after spinning remains in an amorphous state at room temperature. It is easy to maintain, and can exhibit excellent heat resistance and chemical resistance by firmly adhering the bonded materials by softening and flowing due to glass transition, and then crystallizing it.
  • the short fibers of the present invention as binder fibers responsible for adhesion between fibers within a nonwoven fabric, a structure in which aggregate fibers are firmly and uniformly bonded within the nonwoven fabric is formed.
  • the variation in the adhesion rate P b /P m which is the ratio of the outer circumference length P m of the fiber cross section and the bond length P b that is in contact with the bonded part of P m , is 80 % or less.
  • the bonded portion referred to here refers to the portion where the binder fibers that make up the nonwoven fabric soften and flow when heated, thereby bonding adjacent aggregate fibers. - Even if the fiber form before flowing is completely lost, the fiber form may be partially maintained. Note that the above-mentioned variation in the adhesion ratio P b /P m is determined as follows.
  • a cross section of the nonwoven fabric of the present invention is cut out using a razor or the like, and this cross section is photographed using a scanning electron microscope (SEM) at a magnification that allows observation of the entire thickness direction of the nonwoven fabric.
  • SEM scanning electron microscope
  • the length of the outer periphery of the cross section is measured using image analysis software (WINROOF).
  • This value is defined as the outer circumference length P m1 of one fiber, and is expressed in ⁇ m, rounded to the third decimal place.
  • the length of the outer circumference that is bonded to the binder fiber is measured using image analysis software (WINROOF), and this value is defined as the bond length P b1 of one fiber, expressed in ⁇ m to the third decimal place. is rounded off to the nearest whole number.
  • the binder fibers exist in the form of being impregnated between the aggregate fibers due to softening and flow during the thermal bonding process (in some cases, the form as fibers is no longer maintained, but for convenience, (hereinafter also referred to as binder fibers) can be used to identify the interface between aggregate fibers and binder fibers because contrast is obtained due to the difference in unevenness between the aggregate fibers and the binder fibers impregnated there. can do.
  • the bonding rate P bn /P mn of one fiber is calculated as an integer (rounded to the nearest whole number) using the following formula.
  • P bn /P mn (%) P bn ( ⁇ m) / P mn ( ⁇ m) ⁇ 100
  • An integer (unit: %) obtained by rounding off the coefficient of variation obtained by dividing by the average is the variation in the adhesion rate P b /P m in the present invention.
  • the aggregate fibers are bonded uniformly throughout the nonwoven fabric, and as an index of this, the variation in the bonding rate P b /P m is 80%. It is preferable that it is below, and within this range, the proportion of aggregate fibers that are not bonded with binder fibers is small, and it is difficult for aggregate fibers to slip through, so that excellent mechanical properties can be exhibited.
  • the variation in the adhesion rate P b /P m is 60% or less; within this range, the stress can be uniformly borne by the aggregate fibers of the entire nonwoven fabric. can also exhibit excellent mechanical properties.
  • the adhesion ratio P b /P m is 30% or more, the bonding points will be so firmly bonded that the destruction of the sheet-like object will be caused by the destruction of the aggregate fibers themselves, which will affect the mechanical properties of the aggregate fibers. Since the mechanical properties of the sheet-like material can be sufficiently exhibited, this range can be cited as a more preferable range.
  • the method for producing short fibers of the present invention can be produced by cutting long fibers having the characteristic cross-sectional shape of the present invention into a desired length. - Manufactured by bundling tens of thousands of fibers into tow and cutting them into the desired fiber length using a cutting machine such as a guillotine cutter, slicing machine, or cryostat. Regarding the long fibers referred to here, it is also possible to spin fibers made of a single polymer, but there is a problem with operability when using conventional techniques to produce fibers with a short axis length of 2,000 nm or less, which is a feature of the present invention. If yarn is spun without the use of yarn, there may be constraints on the yarn spinning conditions.
  • multilayer laminated fiber means a fiber having a fiber cross section of a multilayer laminated structure in which two or more types of polymers are laminated alternately, in the same order, or in random order. Soluble polymers and easily soluble polymers are not only laminated alternately in one direction, but also laminated radially from the center of the fiber to the outer layer, laminated irregularly in the cross section of the fiber, or , or a combination thereof.
  • the method for spinning the multilayer laminated fiber of the present invention is appropriately selected depending on the manufacturing process in place and the polymer used, but from the viewpoint of excellent productivity, it is preferable to adopt the melt spinning method.
  • Multi-layer laminated fibers produced by the melt-spinning method include, for example, polyethylene terephthalate or its copolymer, polyethylene naphthalate, polybutylene terephthalate, polytrimethylene terephthalate, polypropylene, polyolefin, polycarbonate, polyacrylate, polyamide, polyphenylene sulfide, polylactic acid, thermal It can be made of melt-formable polymers such as plastic polyurethanes. These polymers also contain inorganic materials such as titanium oxide, silica, and barium oxide, carbon black, colorants such as dyes and pigments, flame retardants, optical brighteners, antioxidants, and various additives such as ultraviolet absorbers. May contain.
  • each layer of the multilayer laminated fiber will have irregularities corresponding to the particle size of the fine particles that are the additive, and this will cause the fibers to be generated to have any desired shape. It is possible to provide unevenness.
  • a multilayer laminated fiber is produced by selecting two or more types of polymers from the above polymers and spinning them, but from the viewpoint of forming a stable laminated structure, the combination of polymers is also important.
  • SP value solubility parameters
  • the solubility parameter (SP value) referred to here means a parameter that reflects the cohesive force of a substance defined as (evaporation energy/molar volume) 1/2.
  • SP value means a parameter that reflects the cohesive force of a substance defined as (evaporation energy/molar volume) 1/2.
  • "Plastic Data Book” Asahi Kasei Amidas Corporation/ It can be calculated from the values described in ⁇ Plastics Editorial Department,'' page 189, etc., and the absolute value of the value obtained by subtracting the solubility parameter of one component from the solubility parameter of the other component means the solubility parameter difference in the present invention.
  • the polymers constituting the multilayer laminated fibers may be alkali-ready polyester and alkali-poorly soluble polyester, or alkali-ready polyester and polyfinylene sulfide (poorly alkali-soluble), or alkali-ready polyester and polyamide. (poorly soluble in alkali), short fibers made of a polymer poorly soluble in alkali will be favorably generated by the alkali weight loss treatment.
  • the easily soluble polyester it is preferable to use a polyester obtained by copolymerizing polyethylene glycol and sodium sulfoisophthalate alone or in combination, from the viewpoint of spinnability and easy dissolution in a low concentration aqueous solvent.
  • a polyester obtained by copolymerizing polyethylene glycol and sodium sulfoisophthalate alone or in combination from the viewpoint of spinnability and easy dissolution in a low concentration aqueous solvent.
  • polymers suitable for generating short fibers from multilayer laminated fibers polyethylene terephthalate copolymerized with 5 mol % to 15 mol % of 5-sodium sulfoisophthalic acid as an easily soluble component due to the melting point, and the above-mentioned.
  • polyethylene terephthalate is copolymerized with 5 wt% to 15 wt% of polyethylene glycol having a weight average molecular weight of 500 to 3,000, polyethylene terephthalate as a hardly soluble component, polyphenylene sulfide, or polyamide. -6 may be used.
  • the spinning temperature when spinning the multilayer laminated fiber is the temperature at which the high melting point polymer and high viscosity polymer mainly exhibit fluidity among the two or more types of polymers.
  • the temperature at which this fluidity is exhibited varies depending on the molecular weight, but is preferably set at a temperature from the melting point of the polymer to the melting point +60° C. or lower. If it is less than this, the polymer will not be thermally decomposed in the spinning head or spinning pack, and molecular weight reduction will be suppressed, which is preferable.
  • Stable production can be achieved by setting the discharge rate when spinning multilayer laminated fibers to 0.1 g/min.hole to 20.0 g/min.hole.
  • the ratio of the A component to the B component can be selected in the range of 5/95 to 95/5 in weight ratio of A component/B component based on the discharge amount.
  • a higher proportion of the slightly soluble polymer is preferable from the viewpoint of productivity of flat ultrafine fibers;
  • the component/B component ratio is from 50/50 to 90/10, a multilayer laminated fiber can be stably obtained without a part of the laminated structure being interrupted, and short fibers can be obtained with high production efficiency.
  • the spinneret used here can be a conventionally known composite spinneret that combines two or more types of polymers, but in order to stably form a special multilayer laminated cross section,
  • the following composite base is preferably used.
  • FIG. 4 shows an example using two types of polymers, A component and B component, and if necessary, three or more types of polymers may be used for spinning.
  • composite flow means a fluid whose cross section perpendicular to the flow direction is composed of two or more types of polymers.
  • the fine channels of the composite plate E have a channel configuration that minimizes flow turbulence within the channels, thereby making it possible to produce multilayer laminated fibers.
  • the microchannel described above can be said to have the same characteristics as a conventional static mixer in terms of merging or dividing fluids within the channel, but A static mixer has a flow path designed to mix two types of polymers, and turbulence tends to occur at the interface of the laminated composite flow.
  • a composite nozzle as described above is used. The method used is preferably adopted.
  • the members forming the flow path should be arranged in accordance with the spinning machine and the spinning pack. Just use it.
  • the measuring plate D in accordance with the existing flow path members, the existing spinning pack and its members can be used as they are. For this reason, there is no need to dedicate a spinning machine specifically for this spinneret.
  • the composite flow discharged from the discharge plate F is cooled and solidified, applied with an oil agent, and taken up by a roller having a defined circumferential speed to become composite fibers.
  • This take-up speed may be determined based on the discharge amount and the desired fiber diameter, but it is preferably in the range of 100 to 7,000 m/min in order to stably produce the composite fiber used in the present invention.
  • the fiber is used as a binder fiber that exhibits thermal adhesive properties, it is more preferable to draw it as an undrawn yarn at a speed of 100 to 3,000 m/min.
  • the stretching conditions include, for example, in a stretching machine consisting of one or more pairs of rollers, if the fiber is made of a thermoplastic polymer that can be melt-spun, the first roller is set at a temperature above the glass transition temperature and below the melting point. By adjusting the circumferential speed ratio of the second roller corresponding to the crystallization temperature, the fiber is smoothly stretched in the axial direction of the fiber, heat-set and wound, and a composite fiber having a composite cross section as shown in FIG. 3 can be obtained.
  • the upper limit of the temperature of the first roller is preferably a temperature at which fiber path disturbance does not occur during the preheating process.
  • the degree of crystallinity of the fiber can be maintained low by using it as an undrawn yarn without stretching it.
  • the multilayer laminated fiber used in the present invention can also be manufactured using a spinning method that uses a solvent such as solution spinning. Needless to say.
  • the short fibers of the present invention can be obtained by bundling several dozen to tens of thousands of the obtained multilayer laminated fibers into a tow, cutting the fibers to a desired fiber length, and removing the easily soluble polymer.
  • the multilayer laminated fibers cut to the desired fiber length are immersed in a solvent that can dissolve the easily soluble polymer. Just remove it.
  • a solvent that can dissolve the easily soluble polymer.
  • an alkaline aqueous solution such as an aqueous sodium hydroxide solution can be used.
  • the bath ratio between the multilayer laminated fiber and the alkaline aqueous solution is preferably 1/10,000 to 1/5, more preferably 1/5. ,000 to 1/10. By setting it within this range, it is possible to prevent poor dispersion of lumps due to entanglement of short fibers when dissolving the easily soluble polymer.
  • the alkaline concentration of the alkaline aqueous solution at this time is preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight. Within this range, the dissolution of the easily soluble polymer can be completed in a short time, and the fiber dispersion in which the short fibers of the present invention are homogeneously dispersed can be prepared without unnecessary deterioration of the hardly soluble polymer. Obtainable. Further, the temperature of the alkaline aqueous solution is not particularly limited, but by setting it to 50° C. or higher, the progress of dissolution of the easily soluble polymer can be accelerated.
  • the fiber when it is assumed that the fiber is used as a binder fiber, it is preferable to set the alkaline aqueous solution at 40 to 70° C., since it is possible to accelerate the progress of hydrolysis while maintaining the crystallinity of the fiber at a low level.
  • additives may be used in the fiber dispersion as necessary in order to suppress aggregation and sedimentation of short fibers over time or increase the viscosity of the medium.
  • Types of additives include natural polymers, synthetic polymers, organic compounds, and inorganic compounds.
  • additives that suppress the aggregation of fibers include cationic compounds, nonionic compounds, anionic compounds, and the like.
  • Such additives are preferably used in an amount of 0.001 to 10 equivalents based on the weight of the short fibers. Within this range, sufficient functionality can be provided.
  • the fiber dispersion obtained by the above production method can be used as is. Further, these fiber dispersions may be used by neutralizing the medium with an acid such as hydrochloric acid or acetic acid, or by diluting with water after a dehydration step. It is preferable to make the medium neutral in this way from the viewpoint of ease of handling.
  • the fiber dispersion in which the short fibers of the present invention are homogeneously dispersed in a medium can not only be used as is as a high-performance adsorbent or reinforcing material, but also can be used in wet paper making or spraying.
  • a fiber aggregate from which the medium has been removed using a method it can be used in a wide range of applications such as high-performance filter media, separation membranes, and sound-absorbing materials.
  • Paper is made using a papermaking stock solution in which various short fibers are homogeneously dispersed by putting it into water and stirring it after undergoing a disintegration process or a beating process as necessary.
  • it is possible to adjust the dispersibility by adjusting the amount of short fibers, the amount of aqueous medium, stirring time, etc., and it is preferable to adjust the dispersion state of various short fibers.
  • a dispersant may be included for the purpose of suppressing agglomeration of the short fibers added to the water and producing a nonwoven fabric having a stable dense structure.
  • Types of dispersants include natural polymers, synthetic polymers, organic compounds, and inorganic compounds.
  • additives that suppress the agglomeration of fibers include cationic compounds, nonionic compounds, anionic compounds, etc.
  • the amount of the dispersant added is preferably 0.001 to 10 equivalents relative to the weight of the fibers constituting the nonwoven fabric, and within this range, the processability of wet papermaking will not be impaired.
  • the dispersibility of fibers can be improved, and the nonwoven fabric of the present invention can be manufactured.
  • the various short fibers used in the papermaking stock solution have a fiber length of 0.3 to 30.0 mm. Dispersibility is maintained and wet paper making is possible.
  • the fiber length of the short fibers can be adjusted as appropriate depending on the intended use, but in general, as the fiber length increases, the entanglement between the short fibers increases, which tends to improve the mechanical properties and morphological stability of the nonwoven fabric. However, since the short fibers tend to become entangled and aggregate during stirring in the papermaking stock solution, it is best to adjust it according to the specifications of the short fibers to be mixed into the papermaking stock solution and the expected design.
  • binder fibers in an amount of 5 to 70% by weight.Within this range, the dense structure of the nonwoven fabric can be fixed and the sheet It is possible to improve the strength and the smoothness of the surface of the nonwoven fabric.
  • aggregate fibers may be mixed as other fibers, and the amount can be adjusted as appropriate from 10 to 95% by weight based on the total weight of the nonwoven fabric.
  • the short fibers of the present invention form a bridging structure with the aggregate fibers at both ends, and the short fibers are filled between the aggregate fibers. It is also possible to produce nonwoven fabrics with complex microvoids.
  • the aggregate fibers and binder fibers mentioned here can be selected as appropriate in terms of fiber diameter and fiber cross section depending on the purpose, but they are dense but have complex internal voids, which is a feature of the present invention.
  • the papermaking stock solution prepared from the various short fibers described above After diluting the papermaking stock solution prepared from the various short fibers described above to a certain concentration, it is dehydrated using an inclined wire, a circular screen, etc. to form a nonwoven fabric.
  • Examples of devices used for paper making include cylinder paper machines, Fourdrinier paper machines, inclined short screen paper machines, and paper machines that are a combination of these.
  • the papermaking speed, amount of fibers, and amount of water medium are adjusted according to the desired basis weight, and the accumulation of fibers during drainage is controlled.
  • the sheet-like material formed here undergoes a drying step and a heat treatment step to remove water and bond the binder fibers, thereby producing the nonwoven fabric of the present invention.
  • thermo calendar roll As this drying method, from the viewpoint of drying the sheet and thermally bonding the binder fibers at the same time, it is preferable to use a method using hot air ventilation (air through) or a method in which contact is made with a thermal rotating roll (thermal calendar roll, etc.). be done.
  • the chip-shaped polymer was reduced to a moisture content of 200 ppm or less using a vacuum dryer, and the melt viscosity was measured at a strain rate of 1,216 s ⁇ 1 using Capillograph 1B manufactured by Toyo Seiki.
  • the measurement temperature was the same as the spinning temperature, and the Examples and Comparative Examples have a melt viscosity of 1,216 s -1 . Note that the measurement was performed under a nitrogen atmosphere with a time period of 5 minutes after the sample was placed in the heating furnace until the start of the measurement.
  • the solubility parameter (SP value) is a parameter that reflects the cohesive force of a substance, defined as the square root of (evaporation energy/molar volume), and is a parameter that reflects the cohesive force of a substance, which is defined as the square root of (evaporation energy/molar volume). It can be determined by setting the value of (evaporation energy/molar volume) of the solvent to (evaporation energy/molar volume) of the polymer. The SP value thus determined is described in, for example, "Plastic Data Book” co-edited by Asahi Kasei Amidas Co., Ltd./Plastic Editorial Department, page 189, and this value was used. Further, the solubility parameter difference between the combined polymers was calculated as the absolute value of (SP value of component A ⁇ SP value of component B).
  • Fineness The weight of 100 m of composite fiber was measured, and the value was calculated by multiplying the value by 100. This measurement was repeated 10 times, and the average value was defined as the fineness (dtex). Further, the value obtained by dividing the above fineness by the number of filaments was defined as the single fiber fineness (dtex).
  • This value was taken as the outer circumference length of one fiber, and was expressed as an integer in nm (rounded to the nearest whole number).
  • the area of the inner part surrounded by this outer circumference was measured using image analysis software (WINROOF), and this value was taken as the cross-sectional area of one fiber, and expressed as an integer in nm2 (rounded to the nearest whole number). .
  • WINROOF image analysis software
  • the specific surface area of one fiber was calculated by rounding off to the fifth decimal place according to the formula below.
  • Specific surface area (nm ⁇ 1 ) outer circumference length (nm) / cross-sectional area (nm 2 )
  • the above measurements were performed on 100 fibers to calculate the specific surface area of each fiber, and the arithmetic mean of these was taken as the specific surface area of the present invention.
  • Flatness Length in major axis direction (nm) / Length in short axis direction (nm) The above measurements were performed on 100 fibers to calculate the flatness of each fiber, and the arithmetic mean of these was rounded to the nearest whole number to calculate the flatness.
  • G Average Short Axis Length The arithmetic average of the short axis lengths of the 100 fibers measured above was calculated as an integer in nm (rounded to the nearest whole number).
  • J. Aspect ratio An image is taken at a magnification that allows observation of 10 or more short fibers whose total length can be measured using a microscope.
  • the fiber length of 10 short fibers randomly extracted from an image of the short fibers is measured.
  • the fiber length herein refers to the length of a single fiber in the longitudinal direction from a two-dimensionally photographed image, and is measured by rounding to the second decimal place using image analysis software.
  • the above operation is performed for 10 similarly photographed images, and the arithmetic average of the fiber lengths of 100 fibers is taken as the fiber length of the present invention.
  • the aspect ratio is calculated by rounding off to the nearest whole number according to the following formula.
  • Aspect ratio fiber length (nm) / average short axis length (nm) K.
  • Dispersion index at low speed stirring A fiber dispersion was prepared by dispersing the short fibers in an aqueous medium such that the concentration of short fibers was 0.01% by weight based on the total amount of the fiber dispersion, and after stirring at 100 rpm using a stirrer for 30 seconds. , into a 20 mL screw tube bottle manufactured by As One Co., Ltd.
  • This screw tube bottle was photographed from the side with a digital camera under transmitted illumination, and the obtained image was converted into a monochrome image using image processing software (WINROOF), and a brightness histogram with a series of 256 ( The vertical axis: frequency (number of pixels) and the horizontal axis: brightness (see also FIG. 5) were determined, and the standard deviation of the brightness values in one image was calculated. The same operation was performed on 10 images, the standard deviation of the brightness values of each image was arithmetic averaged, and the value rounded to the second decimal place was used as the dispersibility index at low speed stirring.
  • image processing software WINROOF
  • a fiber dispersion was prepared by dispersing the short fibers in an aqueous medium such that the concentration of short fibers was 0.01% by weight based on the total amount of the fiber dispersion, and the mixture was stirred for 30 seconds at 19,000 rpm using a stirrer. After that, it was placed in a 20 mL screw tube bottle manufactured by As One Co., Ltd. This screw tube bottle was photographed from the side with a digital camera under transmitted illumination, and the obtained image was converted into a monochrome image using image processing software (WINROOF), and a brightness histogram with a series of 256 ( The vertical axis: frequency (number of pixels) and the horizontal axis: brightness (see also FIG.
  • WINROOF image processing software
  • the frequency of the pore size distribution was determined by dividing the values obtained by automatic calculation into class widths of 0.1 ⁇ m, and the value at which the frequency of the pore size distribution was maximum was determined as the maximum frequency. Then, the average of the maximum frequencies of each sample was calculated by converting it into a percentage, and the value obtained by rounding off the second decimal place to the first decimal place was used.
  • the thickness of the nonwoven fabric was measured in mm using a dial thickness gauge SM-114 (manufactured by TECLOCK, measuring point 10 mm ⁇ , scale 0.01 mm, measuring force 2.5 N or less). Measurements were performed at five random locations for each sample, and the average value was rounded to the second decimal place and the thickness of the nonwoven fabric was determined.
  • Nonwoven fabric density Calculated from formula (1) from the basis weight and thickness of the nonwoven fabric. This was determined for 10 samples, and the value obtained by rounding off the simple average value to the third decimal place was taken as the nonwoven fabric density.
  • Ra Arithmetic mean roughness (Ra) of nonwoven fabric surface
  • the surface of the nonwoven fabric was observed using a laser microscope VK-X200 (manufactured by Keyence Corporation), and measured in accordance with JIS B 0601 using analysis software VK-H1XA (manufactured by Keyence Corporation). This was performed at five arbitrary locations for each sample, and the average value was rounded to the third decimal place and the value obtained to the second decimal place was defined as Ra.
  • thermoplastic fiber After weighing out approximately 5 mg of thermoplastic fiber using an electronic balance, the fiber was set in a differential scanning calorimeter (DSC) Q2000 manufactured by TA Instruments, and heated at a heating rate of 16°C/min under nitrogen. , differential scanning calorimetry was carried out under conditions of a measurement temperature range of 50 to 320°C.
  • DSC differential scanning calorimeter
  • the heat of crystallization ⁇ Hc (J/g) was calculated from the area of the exothermic peak in the obtained measurement results (DSC curve), and the heat of crystallization ⁇ Hm (J/g) was calculated from the area of the endothermic peak.
  • ⁇ Hc and ⁇ Hm were calculated from the sum of the areas of all the peaks. Measurement was performed three times by changing the measurement position for each level, and the arithmetic mean was obtained to calculate ⁇ Hc and ⁇ Hm, and then the degree of crystallinity was calculated by rounding to the first decimal place using the following formula.
  • Crystallinity (%) ( ⁇ Hm- ⁇ Hc)/ ⁇ Hm 0 ⁇ 100 Note that ⁇ Hm 0 referred to here is the heat of fusion of a complete crystal (J/g), and in the case of PET, 140.1 (J/g) was used, and in the case of PPS, 146.2 (J/g) was used. .
  • V Variation in adhesion rate/adhesion rate Cut out a cross section of the nonwoven fabric with a razor, etc., and use a scanning electron microscope S-5500 (SEM) manufactured by Hitachi High-Technologies Corporation at a magnification that allows the entire thickness direction of the sheet to be observed. Photographed at. Regarding the cross section of one aggregate fiber present in the photographed image, the length of the outer periphery of the cross section was measured using image analysis software (WINROOF). This value was defined as the outer circumference length P m1 of one fiber, and was expressed in ⁇ m, rounded to the third decimal place.
  • WINROOF image analysis software
  • the length of the outer circumference that is bonded to the binder fiber is measured using image analysis software (WINROOF), and this value is defined as the bond length P b1 of one fiber, expressed in ⁇ m to the third decimal place. is rounded off.
  • the binder fibers exist in the form of being impregnated between the aggregate fibers due to softening and flow during the thermal bonding process, but between the aggregate fibers and the binder fibers impregnated therein, The interface between aggregate fibers and binder fibers was identified by the contrast obtained by the difference in unevenness.
  • the adhesive rate P bn /P mn of one fiber was calculated as an integer (rounded to the nearest whole number) using the following formula.
  • P bn /P mn (%) P bn ( ⁇ m) / P mn ( ⁇ m) ⁇ 100
  • the standard deviation is calculated in the same way, and the coefficient of variation obtained by dividing the standard deviation by the arithmetic mean is expressed as an integer in %, rounded to the nearest whole number, and the value is the adhesion rate P b /P m in the present invention.
  • Example 1 As component A, polyethylene terephthalate (PET, melt viscosity: 120 Pa ⁇ s, melting point: 254°C, SP value: 21.4 MPa 1/2 ); as component B, 8.0 mol% of 5-sodium sulfoisophthalic acid, polyethylene Polyethylene terephthalate (SSIA-PEG copolymerized PET, melt viscosity: 95 Pa ⁇ s, melting point: 233°C, SP value: 22.9 MPa 1/2 ) copolymerized with 9 wt % glycol was prepared. Note that the difference in solubility parameters between these polymers is 1.5 MPa 1/2 .
  • the composite ratio of the A/B components was set to 80/20, and the mixture was made to flow into a spinning pack equipped with a composite nozzle as shown in FIG. vomited out.
  • the composite plate uses a microchannel G that can alternately stack both components in 128 layers, and discharges the two types of polymers in a composite form in which multiple layers are alternately stacked in one direction as shown in Figure 3. did.
  • an oil agent was applied thereto, and it was wound up at a spinning speed of 1,000 m/min to collect an undrawn yarn of 200 dtex-24 filaments (total discharge rate 20 g/min).
  • the wound undrawn fiber was drawn 3.6 times between rollers heated to 90°C and 130°C to obtain a drawn fiber of 56 dtex-24 filaments.
  • the obtained multilayer laminated fiber was cut to have a fiber length of 0.6 mm, and the cut multilayer laminated fiber was heated to 90°C in a 1% by weight sodium hydroxide aqueous solution (bath ratio 1/100) for 30 minutes.
  • a 1% by weight sodium hydroxide aqueous solution bath ratio 1/100
  • the cross-sectional form was a ribbon-like cross section in which the lengths of the long and short axes were significantly different, the flatness was 80, and the average length of the short axes was 188 nm. Further, the variation in the length of the short axis of the cross section was 36%, and the degree of unevenness was 30%, indicating that the length of the short axis had a moderate variation, and the surface had a moderate amount of unevenness. Further, the degree of crystallinity was 36%, indicating that crystallization had sufficiently progressed, and the melting point was 254°C.
  • a fiber dispersion liquid was prepared by dispersing these short fibers in an aqueous medium so that the short fiber concentration was 0.01% by weight based on the total amount of the fiber dispersion liquid, and the dispersion state after stirring at each speed was image-processed. Evaluated by. At this time, if the fiber dispersion is homogeneous, there will be no big difference in brightness and darkness, so the standard deviation of brightness (dispersion index) will be small, but if the fiber dispersion is heterogeneous, there will be a local separation of brightness and darkness. The standard deviation (dispersion index) of brightness increases.
  • Example 2 The method described in Example 1 was changed to a composite plate having microchannels in which both components were alternately laminated in 64 layers (Example 2), 32 layers (Example 3), and 16 layers (Example 4).
  • the same procedure as in Example 1 was carried out except for the following.
  • These multilayer laminated fibers were subjected to the same cutting and dissolving treatment as described above to obtain short fibers with a flat cross-sectional shape as shown in FIG.
  • the evaluation results of these short fibers are shown in Table 1, and in all of Examples 2 to 4, they had a larger specific surface area than ordinary ultrafine fibers, and their cross-sectional shapes were It was in the form of an extremely thin ribbon with high flatness, and had moderate variation in short axis length and unevenness.
  • Example 1 Compared to Example 1, as the flatness decreases and the average short axis length increases, the dispersion index at low and high speed stirring becomes slightly larger, but the specific surface area of short fibers and excellent dispersibility are improved. The goal was to achieve both. Further, the crystallinity of the short fibers was 36% and the melting point was 254°C.
  • Example 5 The method described in Example 1 was carried out in the same manner as in Example 1, except that a composite plate having microchannels in which both components were alternately laminated in 512 layers (Example 5) was used.
  • This multilayer laminated fiber was subjected to the same cutting and dissolving treatment as described above to obtain short fibers with a flat cross-sectional shape.
  • the evaluation results of this short fiber are shown in Table 1, and it has an extremely large specific surface area that far exceeds that of nanofibers with a fiber diameter of several hundred nanometers, and its cross-sectional shape is ultrathin with extremely high flatness. It was in the shape of a ribbon.
  • the dispersion index at low speed was 5 and the dispersion index at high speed was 18.Although the dispersion index increases with high speed stirring, there was no problem of clumpy dispersion, and the short fibers were very small. It achieved both a large specific surface area and excellent dispersibility. Further, the crystallinity of the short fibers was 36% and the melting point was 254°C.
  • Example 1 In the method described in Example 1, a spinning pack for 15 filaments incorporating a 1,000-island type sea-island composite spinneret in which the A component is an island component and the B component is a sea component is used. Everything was carried out in the same manner as in Example 1 except that the ratio was set to 50/50 and the total discharge amount was 42 g/min.
  • This sea-island composite fiber was subjected to the same cutting and dissolving treatment as described above to obtain nanofibers with a round cross section (crystallinity: 36%, melting point: 254°C). The evaluation results of this nanofiber are shown in Table 1. Although the specific surface area was large, high-speed stirring caused poor dispersion in the form of lumps in which the fibers were entangled with each other, and the dispersibility was evaluated to be extremely low.
  • Comparative example 2 The method described in Comparative Example 1 was carried out in the same manner as in Comparative Example 1 except that the cross-sectional shape of the island component was made into a flat cross-section. Although nanofibers with a large specific surface area and a flat cross section (crystallinity: 36%, melting point: 254°C) were obtained, since the flatness was low, the fibers could be separated by high-speed stirring as in Comparative Example 1. were intertwined, and the dispersibility was extremely low.
  • Example 6, 7 In the method described in Example 1, everything was carried out in the same manner as in Example 1 except that a composite plate having a different channel configuration from the microchannel G was used (Examples 6 and 7).
  • the evaluation results of the obtained short fibers are shown in Table 2. Although they had an ultra-thin cross-sectional shape with high flatness similar to Example 1, due to the change in the flow path configuration of the composite plate, the short fibers were shortened. It was homogeneous with small variations in shaft length and small irregularities.
  • the dispersion index was evaluated, the value of the dispersion index was slightly larger than in Example 1 because the variation in short axis length and unevenness were smaller than in Example 1, but there was no noticeable lumpy dispersion defect. was not observed, indicating excellent dispersibility. Further, the crystallinity of the short fibers was 36% and the melting point was 254°C.
  • Example 8 9 In the method described in Example 1, everything was carried out in the same manner as in Example 1 except that the fiber length was cut to 1.8 mm (Example 8) and 5.0 mm (Example 9).
  • Example 8 even when the aspect ratio was large, due to the dispersion effect derived from the cross-sectional shape, the fibers did not become entangled with each other and the dispersibility was excellent.
  • Example 9 the aspect ratio was even larger than in Example 8, so that the dispersibility under high-speed stirring tended to deteriorate somewhat, but no problematic lump-like dispersion was observed. , which achieved both the specific surface area of short fibers and excellent dispersibility. Further, the crystallinity of the short fibers was 36% and the melting point was 254°C.
  • Comparative example 4 In the method described in Comparative Example 1, everything was carried out in the same manner as in Comparative Example 1 except that the fiber length was cut to 5.0 mm. In Comparative Example 4, since the aspect ratio was larger than that in Comparative Example 1, the fibers were significantly entangled with each other even at low speed stirring, resulting in poor dispersion in the form of lumps, resulting in significantly poor dispersibility. Further, the crystallinity of the short fibers was 36% and the melting point was 254°C.
  • the A component is polyethylene terephthalate (PET, melting point: 254°C), and the B component is composed of polyethylene terephthalate (SSIA-PEG copolymerized PET) copolymerized with 8.0 mol% of 5-sodium sulfoisophthalic acid and 9 wt% of polyethylene glycol.
  • PET polyethylene terephthalate
  • SSIA-PEG copolymerized PET polyethylene terephthalate copolymerized PET copolymerized with 8.0 mol% of 5-sodium sulfoisophthalic acid and 9 wt% of polyethylene glycol.
  • a multilayer laminated fiber in which two types of polymers were alternately laminated in one direction as shown in Figure 3 was cut to a fiber length of 0.6 mm, and this multilayer laminated fiber was heated to 90°C.
  • a dispersion containing flat fibers with flatness of 20 (minor axis length: 1,000 nm) as functional fibers was obtained. Obtained. The degree of crystallinity of the obtained flat fiber was 36%, indicating that crystallization had sufficiently progressed, and the melting point was 254°C.
  • heat-fusible core-sheath composite fiber (core component: PET, sheath component: terephthalic acid 60 mol%, isophthalic acid 40 mol%, ethylene glycol 85 mol%, diethylene glycol 15 mol% copolymerized and melting point 110) was used.
  • °C polyester (copolymerized polyester)) cut fibers (core component fiber diameter 10 ⁇ m, fiber length 5.0 mm) were prepared to a mixing ratio of 30% by weight, and the mixing ratio with water was adjusted in the defibration and beating steps.
  • a papermaking stock solution was prepared by uniformly mixing and dispersing a flat fiber dispersion liquid adjusted to 70%.
  • this paper making stock solution was made into paper with a basis weight of 50 g/ m2 , and then placed in a rotary dryer with the roller temperature set at 110°C.
  • a nonwoven fabric was obtained by drying and heat treating.
  • the obtained nonwoven fabric had a uniform orientation of flat fibers, a dense structure in the cross-sectional direction, a thickness of 105 ⁇ m, and a nonwoven fabric density of 0.48 g/cm 3 .
  • the average pore size calculated by the bubble point method was 0.5 ⁇ m, the maximum frequency of pore size distribution was 17.9%, and the nonwoven fabric was formed with dense spaces having various micropores.
  • Ra was 2.96 ⁇ m and the surface was smooth.
  • the sound absorption coefficient at 1,000 Hz was 82%, indicating that the nonwoven fabric had excellent sound absorption properties in the low frequency band. The results are shown in Table 3.
  • Example 10 was carried out except that the basis weight of the nonwoven fabric was changed to 25 g/m 2 (Example 11) and 5 g/m 2 (Example 12).
  • Example 10 the obtained nonwoven fabric had flat fibers (crystallinity: 36%, melting point: 254°C) with uniform orientation and a dense structure in the cross-sectional direction.
  • the evaluation results of these nonwoven fabrics are shown in Table 3.
  • the basis weight is decreased, the density of the nonwoven fabric decreases and the average pore size increases, so the density decreases compared to Example 10. Ta.
  • the sound absorption coefficient at 1,000 Hz was 66% or more in all cases, and the nonwoven fabrics had excellent sound absorption properties that were effective even in practical use.
  • Examples 13 to 15 As shown in Table 3, the procedure was carried out in accordance with Example 10, except that the flatness and short axis length of the functional fibers (flat fibers) constituting the nonwoven fabric were variously changed (Examples 13 to 15).
  • the obtained nonwoven fabric had flat fibers (crystallinity: 36%, melting point: 254°C) with uniform orientation and a dense structure in the cross-sectional direction, as in Examples 10 to 12.
  • the evaluation results of these nonwoven fabrics are shown in Table 3.
  • the density of the nonwoven fabric increases and the average pore size increases, so the density is lower than that of Example 10. It was an improvement.
  • the maximum frequency of pore size distribution was decreased, and the nonwoven fabric had a more complex pore structure.
  • the short axes of the flat fibers were shortened, resulting in a decrease in Ra, and the nonwoven fabric had a smaller surface roughness than Example 10.
  • Example 10 was carried out except that the flatness of the flat fibers constituting the nonwoven fabric was changed to 10.
  • the obtained nonwoven fabric had flat fibers aligned in the same direction as in Examples 10 to 15, and had a dense structure in the cross-sectional direction.
  • the evaluation results of this nonwoven fabric are shown in Table 3.
  • the flatness is decreased compared to Example 10, the nonwoven fabric density increases and the average pore size increases. Although it was slightly lower, there was no problem in practical use and it met the requirements for the nonwoven fabric of the present invention.
  • the results are shown in Table 3. Further, the crystallinity of the flat fibers was 36% and the melting point was 254°C.
  • Example 17 The flat fibers used in Example 10 (crystallinity: 36%, melting point: 254°C) were used as the functional fibers constituting the nonwoven fabric, and the binder fibers used in Example 10 and other fibers with a fiber diameter of 0 were used. .
  • the obtained nonwoven fabric has a dense structure in which the short axes of the flat fibers overlap perpendicularly to the thickness direction as in Examples 10 to 16, and the ultrafine fibers exist in a bridge-like manner using aggregate fibers as scaffolds. had.
  • the evaluation results of this nonwoven fabric are shown in Table 3, and the nonwoven fabric had a more dense structure than Example 10 due to the presence of the ultrafine fibers in a bridged manner.
  • the pore structure was made uniform by the ultrafine fibers, and the maximum frequency of pore size distribution was higher than in Example 10.
  • Example 17 in addition to the densification of the nonwoven fabric structure by the flat fibers mixed as functional fibers, the structure was such that ultrafine fibers mixed as other fibers were placed in the voids, resulting in an extremely excellent structure. It showed sound absorption properties. Furthermore, it has a small pore size and a special pore structure, so it can be expected to exhibit excellent properties in terms of performance such as filtration and separation.
  • Example 10 was carried out except that the fibers (aggregate fibers) constituting the nonwoven fabric were changed to ultrafine fibers (PET, crystallinity: 36%, melting point: 254°C) with a fiber diameter of 3.0 ⁇ m.
  • the obtained nonwoven fabric has a thickness of 220 ⁇ m, a nonwoven fabric density of 0.23 g/cm 3 , and an average pore size calculated by the bubble point method of 14.3 ⁇ m, which means that it has a low density with coarse voids present compared to Example 10. It was a non-woven fabric. Moreover, Ra was 13.62 ⁇ m and the surface was rough. The results are shown in Table 4.
  • Example 5 As the fibers constituting the nonwoven fabric, the ultrafine fibers with a fiber diameter of 3.0 ⁇ m are used as the aggregate fibers, and the flat fibers used in Example 10 (crystallinity: 36%, melting point: 254 ° C.) are used as the functional fibers.
  • the obtained nonwoven fabric has a low mixing ratio of flat fibers, so the thickness is 197 ⁇ m, the nonwoven fabric density is 0.25 g/cm 3 , and the average pore size calculated by the bubble point method is 12.3 ⁇ m, which is coarse as in Comparative Example 4. It was a nonwoven fabric with low density and voids. The results are shown in Table 4.
  • Example 10 was carried out except that the flatness of the flat fibers constituting the nonwoven fabric was set to 2.
  • the flat fibers had a crystallinity of 36% and a melting point of 254°C.
  • the obtained nonwoven fabric has a thickness of 264 ⁇ m, a nonwoven fabric density of 0.19 g/cm 3 , and an average pore size calculated by the bubble point method of 29.6 ⁇ m, which is even coarser than Comparative Examples 4 and 5 because the flatness of the flat fibers is small. It was a nonwoven fabric with low density and voids. The results are shown in Table 4.
  • component A is polyethylene terephthalate (PET)
  • component B is composed of polyethylene terephthalate (SSIA-PEG copolymerized PET) copolymerized with 8.0 mol% of 5-sodium sulfoisophthalic acid and 9 wt% of polyethylene glycol.
  • Multilayer laminated fibers in which two types of polymers are alternately laminated in one direction as shown are obtained, and cut processing is performed so that the fiber lengths are 1.0 mm (Example 19) and 5.0 mm (Example 20).
  • the B component was eluted from each of the multilayer laminated fibers in the same manner as in Example 10 to obtain a dispersion containing flattened fibers (minor axis length: 500 nm) with flatness of 40 and different fiber lengths. Utilizing this dispersion liquid, paper was made to have a basis weight of 5.0 g/m 2 in the same manner as in Example 12.
  • the obtained nonwoven fabric has flat fibers (crystallinity: 36%, melting point: 254°C) with uniform orientation and a dense structure in the cross-sectional direction, and although it is extremely thin, it has excellent functionality. As the length of the fibers increased, the rigidity of the sheet increased, and the smoothness of the sheet surface also improved. The results are shown in Table 5.
  • Example 21 As component A, polyethylene terephthalate (PET, melt viscosity: 120 Pa ⁇ s, melting point: 254°C, SP value: 21.4 MPa 1/2 ); as component B, 8.0 mol% of 5-sodium sulfoisophthalic acid, polyethylene Polyethylene terephthalate (SSIA-PEG copolymerized PET, melt viscosity: 95 Pa ⁇ s, melting point: 233°C, SP value: 22.9 MPa 1/2 ) copolymerized with 9 wt % glycol was prepared. Note that the difference in solubility parameters between these polymers is 1.5 MPa 1/2 .
  • the composite ratio of the A/B components was set to 80/20, and the mixture was made to flow into a spinning pack equipped with a composite nozzle as shown in FIG. vomited out.
  • the composite plate uses a microchannel G that can alternately stack both components in 64 layers, and discharges the two types of polymers in a composite form in which multiple layers are alternately stacked in one direction as shown in Figure 3. did.
  • an oil agent was applied thereto, and it was wound up at a spinning speed of 1,000 m/min to collect an undrawn yarn of 100 dtex-24 filaments (total discharge rate of 10 g/min).
  • the obtained multilayer laminated fiber was cut to have a fiber length of 5.0 mm, and the cut multilayer laminated fiber was heated to 70°C in a 1% by weight sodium hydroxide aqueous solution (bath ratio 1/100) for 30 minutes.
  • a 1% by weight sodium hydroxide aqueous solution bath ratio 1/100
  • SSIA-PEG copolymer PET which is an easily soluble polymer
  • the cross-sectional form is a ribbon-like cross section with significantly different lengths of the long and short axes, with an oblateness of 40, a short axis of 500 nm, and a long axis of 20,000 nm. Ta. Further, the variation in the length of the short axis of the cross section was 32%, and the degree of unevenness was 21%, indicating that the length of the short axis had a moderate variation, and the surface had a moderate amount of unevenness. Further, the crystallinity was 6%, which was an amorphous state, and the tan ⁇ was 0.25, indicating high fluidity.
  • the obtained nonwoven fabric was free of aggregates such as fiber lumps and had a good texture, and although it was thin and had a low basis weight, it had a good strength of 2.40 N/15 mm.
  • the results are shown in Table 6.
  • Example 22, 23 In the method described in Example 21, everything was the same as in Example 21 except that the composite plate was changed to a composite plate having fine channels in which both components were laminated in 32 layers (Example 22) and 16 layers (Example 23). carried out. These multilayer laminated fibers were subjected to the same cutting and melting treatment as described above to obtain short fibers (melting point: 254° C.) with a flat cross-sectional shape as shown in FIG. The evaluation results of these short fibers are shown in Table 6. Examples 22 and 23 had a large specific surface area, and the cross-sectional shape was an extremely thin ribbon with high flatness. , which had appropriate short axis length variations and unevenness.
  • Example 24, 25 In the method described in Example 22, everything was carried out in the same manner as in Example 22, except that the temperature of the dissolution treatment when removing the easily soluble polymer was 75 ° C. (Example 24) and 80 ° C. (Example 25). did.
  • the evaluation results are shown in Table 6, and as compared to Example 22, the crystallinity of the short fibers (melting point: 254°C) increased and the tan ⁇ decreased due to the higher melting temperature. .
  • the degree of crystallinity was higher and the fluidity was lower than in Example 22, resulting in a lower adhesion rate and increased variation in the adhesion rate, but it maintained excellent strength.
  • Example 26, 27 In the method described in Example 22, everything was carried out in the same manner as in Example 22, except that a composite plate having a different channel configuration from the microchannel G was used. The obtained results are shown in Table 6. Although it had an extremely thin cross-sectional shape with high flatness similar to Example 22, due to the change in the channel configuration of the composite plate, the length of the minor axis was Short fibers with a cross section with small variations (Example 26) and short fibers with a cross section with a small unevenness (Example 27) were obtained.
  • component A is polyphenylene sulfide (PPS, melt viscosity: 130 Pa ⁇ s, melting point: 283°C, SP value: 25.8 MPa 1/2 ) consisting only of p-phenylene sulfide units.
  • component B was made into polyethylene terephthalate (SSIA copolymerized PET, melt viscosity: 130 Pa ⁇ s, melting point: 245°C) copolymerized with 5.0 mol% of 5-sodium sulfoisophthalic acid, and was discharged at 310°C.
  • the obtained undrawn yarn was immersed in a 3% by weight aqueous sodium hydroxide solution (bath ratio 1/100) heated to 60°C for 40 minutes for dissolution treatment, and the easily soluble polymer SSIA copolymerized PET was dissolved at 99% or more. By dissolving and removing the fibers, short fibers having a flat cross section as shown in FIG. 1 were obtained.
  • DY-1125K quaternary ammonium salt type cationic surfactant manufactured by Lion Specialty Chemicals Co., Ltd. was added as a solubility promoter at a rate of 0.5% based on the mass of the sodium hydroxide aqueous solution. % by weight was added.
  • thermoplastic fibers as the binder fibers and 50% by mass of the short fibers obtained in Reference Example 2 as the aggregate fibers of the bonded material were mixed into the papermaking dispersion, and the fiber concentration was 0. .4% by mass.
  • This paper making liquid was supplied to a simple paper machine to obtain a wet nonwoven fabric with a basis weight of 5 g/m 2 .
  • thermocompression bonding was performed for 1 minute at a press pressure of 1.0 MPa using a flat plate heating press machine at 220°C.
  • Examples 28 and 29 have a large specific surface area, and the cross-sectional shape is different from the flatness. It was in the form of a tall, ultra-thin ribbon, with moderate variation in short axis length and unevenness. When evaluated as a nonwoven fabric, it was found to be uniform with no fiber lumps in the nonwoven fabric, have a high adhesion rate, have low variation in the adhesion rate, and have excellent strength.
  • Example 30 In the method described in Example 28, everything was carried out in the same manner as in Example 28, except that the temperature of the dissolution treatment when removing the easily soluble polymer was 90°C.
  • the evaluation results are shown in Table 7, and as compared to Example 28, the crystallinity of the short fibers (melting point: 283°C) increased and the tan ⁇ decreased due to the higher melting temperature. .
  • the degree of crystallinity was higher than in Example 28, so the adhesion rate decreased and the variation in the adhesion rate increased, but excellent strength was maintained.
  • A Short fiber B: A component C: B component D: Measuring plate E: Composite plate F: Discharge plate G: Fine channel
  • the fiber dispersion in which the short fibers of the present invention are homogeneously dispersed in a medium be used as a high-performance adsorbent or reinforcing material, but also the dispersion can be used in a medium by wet papermaking or spraying. If it is removed and made into sheets, it can be used in a wide range of industrial materials such as high-performance filter media, separation membranes, and sound-absorbing materials.

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Abstract

La présente invention fournit des fibres courtes dans lesquelles la planéité, qui est la valeur obtenue en divisant la longueur de l'axe majeur par la longueur de l'axe mineur d'une section transversale de chaque fibre, est de 5 ou plus, et la moyenne des longueurs des axes mineurs est de 2 000 nm ou moins.　La présente invention concerne des fibres courtes qui présentent une excellente dispersibilité dans un milieu liquide ; et la présente invention fournit des fibres courtes qui ne s'entremêlent pas les unes aux autres même dans des conditions d'agitation dans une large plage, et sont appropriées pour l'obtention d'un liquide dispersé de fibres homogènes.
PCT/JP2023/020061 2022-06-13 2023-05-30 Fibres courtes, liquide dispersé dans des fibres et tissu non tissé WO2023243396A1 (fr)

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